What specific model of 56" DLP are you looking at? Also LED DLP's are fairly new so you might not get a lot of response from people who have real world gaming experience on one...especially pc gaming. I know that the earlier DLP's didn't handle gaming as well as lcd/plasma but I have no idea about the current generation.
The only thing I can tell you is this is a model from 2005. It was the original LED DLP product on the market. Amazon customers seem to love this one and it is at a very good price even for a DLP product. Amazon probably got a real good deal from Samsung for purchasing the whole lot of what was left in the warehouse. A DLP is not as sharp as a LCD or Plasma but offers a lower price alternative for a big screen. If you are 6 to 10 feet away from the screen I do not think you would have any problem with a DLP product but if you are looking for a replacement for a monitor forget it. As for this particular model, I have no knowledge of its quality but I do know that it was a current model for about 2 years before it was discontinued.
I have a 52" Mitsu DLP, not an LED, I hooked it up to my main computer and played a few games on it, was enjoyable and fun, I have my Wii hooked up to it and love it. The resolution and smoothness was very good from the computer, the Wii is only 480p so cant really speak for overall quality of that picture but its very fun. I dont know anyone who owns one of the LED DLP's, Might try googleing to see what people think about it.